1. Field of the Invention
The present invention relates in general to the field of optical storage, and more particularly to an apparatus and method for layer jump braking control in an optical drive.
2. Description of the Prior Art
Optical disks are popular storage media nowadays. The data capacity of an optical disk depends on layer properties and the number of layers (single or dual layer). When an optical drive reads a dual layer disk, the optical drive performs a layer jump process, that is, the pick up head of the optical drive moves its laser spot between two layers of the disk. In this specification, these two layers are called layer 0 and layer 1 respectively.
FIG. 1 is an architectural diagram of a conventional optical drive with layer jump control. The conventional optical drive includes a pick up head 11, a pre-amp 12, a controller 13, a driver 14, and a switch 15, as shown in FIG. 1. The switch 15 is used for controlling whether to perform the layer jump process according to a layer jump control signal.
FIG. 2 is a diagram showing how to perform layer jump control according to the architecture of FIG. 1. Before the layer jump process is performed (i.e. a layer jump control signal has not been received yet), the driver 14 receives the focusing control signal from the controller 13 and generates the driving force according to the focusing control signal such that the laser spot of the pick up head 11 is kept at the original layer (layer 0 in FIG. 2). In this way, closed-loop focusing control is achieved. Since the layer distance of the disk 16 is not uniform and a wobble effect may occur, the focusing control signal varies correspondingly, as shown in FIG. 2.
When receiving the layer jump control signal, the switch 15 is turned to the lower node of FIG. 1, and the layer jump process is then performed. As shown in FIG. 2, the driver 14 receives a kicking signal, a holding signal, and a braking signal in turn so as to make the pick up head 11 to correspondingly perform a kicking process, a holding process, and a braking process. The kicking process moves the laser spot away from the original layer and toward the target layer (layer 1 in FIG. 2). The holding process keeps the pick up head 11 moving toward the target layer continually after the laser spot completely escapes the original layer. When the laser spot approaches the focusing linear region of the target layer, the braking process slows down the pick up head 11 to prevent the laser spot from exceeding the linear region, thereby avoiding layer jump failure. When the braking process is finished, the whole layer jump process is also finished, and the switch 15 is shifted back to the upper node to return to the original closed-loop focusing control. The braking signal of the conventional optical drives is constant, that is, the braking control force outputted from the driver 14 is fixed when the layer jump process is performed.
However, a problem exists in this implementation. Since the layer distance of a dual layer disk may not be uniform, and the disk may wobble when accessed by the disk drive, the layer jump location and speed would not be all the same. If a fixed braking control force is applied, it is very possible that the laser spot exceeds the focusing linear region of the target layer to cause the layer jump failure. In consideration of different optical disks, the variation is still larger, and layer jump failure is even more likely to occur.
The other prior arts are disclosed. For example, U.S. Pub. No. 20030112720 titled “Method of layer jump braking control for an optical drive” and U.S. Pub. No. 20030076755 titled “Layer jump control for an optical drive”.